Single screw compressors have been used as compressors for compressing a refrigerant or air. For example, Japanese Patent Publication No. H06-042474 discloses a single screw compressor including a screw rotor, and two gate rotors.
The single screw compressor will be described below. The screw rotor is substantially in the shape of a column, and a plurality of helical grooves are formed in an outer peripheral surface thereof. Each of the helical grooves is opened in the outer peripheral surface of the screw rotor. Start ends of the helical grooves are opened at one of end faces of the screw rotor. Each of the gate rotors is substantially in the shape of a flat plate, and is arranged laterally adjacent to the screw rotor. The gate rotor includes a plurality of rectangular plate-shaped gates which are radially arranged. The gate rotor is arranged with an axis of rotation thereof perpendicular to an axis of rotation of the screw rotor, and the gates mesh with the helical grooves of the screw rotor.
The screw rotor and the gate rotors of the single screw compressor are contained in a casing. In the casing, low pressure space into which uncompressed, low pressure fluid flows is formed. When the screw rotor is rotated by an electric motor etc., the gate rotors are rotated by the rotation of the screw rotor. Thus, the gates of the gate rotors move relatively from the start ends (ends through which the fluid is sucked) to terminal ends (ends through which the fluid is discharged) of the helical grooves.
In a suction phase during which the low pressure fluid is sucked into fluid chambers formed by the helical grooves of the screw rotor, the low pressure fluid flows into the fluid chambers through the outer peripheral surface and the end face of the screw rotor. Then, each of the fluid chambers is divided from the low pressure space by a divider wall (an inner cylindrical wall) of the casing which covers the outer peripheral surface of the screw rotor, and the gate which enters the helical groove. In a compression phase during which the fluid in the fluid chamber is compressed, the gate moves relatively from the start end to the terminal end of the helical groove, thereby reducing a volume of the fluid chamber. Thus, the fluid in the fluid chamber is compressed.